15.5 Structure and function of synapses Flashcards
What is a synapse
The point where one neurone communicates with another or with an effector
So they link neurones together so therefore coordinating activities
What are neurotransmitters
Chemicals used to transmit information from one synapse to another.
This is because there is a small gap between neurones
What is the synaptic cleft
It is a small gap between neurones
What is the presynaptic neurone
What is synaptic knob and what does it contain
The neurone that releases the neurotransmitter
The axon of this neurone ends in a swollen portion called the synaptic knob.
This contains lots of mitochondria and large amounts of endoplasmic reticulum which are required to make the neurotransmitter
What are synaptic vesicles
What is post synaptic neurone
Where the neurotransmitters are stored .
It is then released from vesicles and it diffuses across the postsynaptic neurone which possesses specific receptor proteins on its membrane to receive it
One feature of a synapse is undirectionality
Explain this
Synapses only pass information in one direction
From presynaptic neurone to the postsynaptic neurone.
Synapses act as valves
One feature of a synapse is summation
Explain this
Low frequency action potentials often lead to the release of insufficient concentrations of neurotransmitter to trigger a new action potential in the post synaptic neurone.
This means there is a rapid build up of neurotransmitter in the synapse by one of two methods
What is spacial summation
A number of different presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the postsynaptic neurons.
So together they trigger an action potential
What is temporal summation
A single presynaptic neurone releases neurotransmitter many times over a very short period. So frequency increases.
If the concentration of neurotransmitter exceeds the threshold value of the postsynaptic neurone, then a new action potential is triggered.
What are inhibitory synapses
They make it unlikely that a new action potential will be created on the postsynaptic neurone
How do inhibitory synapses work
- Presynaptic neurone releases type of neurotransmitter that binds to chloride ion protein channels on the postsynaptic neurone
- The neurotransmitter causes chloride ion channels to open
- Chloride ions diffuse in facilitated through these channels
-The binding of the neurotransmitter causes potassium protein channels to open
- Potassium ions move out of postsynaptic neurone into the synapse
- This combined effect of negatively charged Cl- ions entering and K+ ions leaving polarise the inside of postsynaptic membrane so it is more negative and the outside is more positive.
- Membrane potential increases to -80mv compared with the usual -65mv at resting potential
- Hyperpolarisation occurs so it is less likely that a new action potential will be created as more sodium ions will need to enter.
Overall describe process of neurotransmitters across synapse
They are made in presynaptic neurone and travel to postsynaptic neurone
They are stored in synaptic vesicles. When action potential reaches synaptic knob the membranes of these vesicles fuse with presynaptic membrane to release neurotransmitter
When released, neurotransmitter diffuses along synaptic cleft to bind to specific receptors on post synaptic neurone
When they bind this makes a new action potential in postsynaptic neurone.
What are excitatory synapses
Synapses that produce new action potentials
How can a single impulse create lots of responses
A single impulse along one neurone to initiate new impulses in a number of different neurones at a synapse.
This allows a single stimulus to create lots of simultaneous responses
What does allowing lots of impulses be combined at a synapse do
Allow nerve impulses from receptors reacting to different stimuli to contribute to a single response.
